In Steuben's Regulations for the Order and Discipline of the Troops of the United States he has this to say in the section of Instructions.
Instructions for the Captain
He must divide his company into four squads, placing each under the particular care of a non-commissioned officer, who is to be answerable for the dress and behaviour of the men of his squad.
Steuben's regulations went into effect in the spring-summer of 1779. Whether the divying up into 4 squads predates the regulations is not known to me. What is clear from the Regulations is that a company was divided into 4 squads. There were no platoons (in fact the regulations seem to use platoon and company interchangeably as Wright indicated).
The Lieutenants and Ensigns had other duties, none of which related to command a subunit of the company.
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